Recently, for example in automotive fields, the use of high strength steel sheets is increasing, and the strength of the high strength steel sheets employed is becoming higher and higher, in order to reduce vehicle weight and improve collision safety.
When such high strength steel is employed, spot welding, primarily using resistance welding, is employed in vehicle body assembly and component attachment processes.
Since spot welding requires electrodes to be pressed from both face sides of the steel sheets, it is not applicable to members with closed cross-section structures and the like. Arc spot welding (also known as plug welding) using arc welding is therefore employed at locations where spot welding is not possible.